1. Field of the Invention
The present invention relates to a rechargeable lithium battery, more particularly to a rechargeable lithium battery having excellent cycle-life characteristics and stability.
2. Description of the Related Art
A lithium rechargeable battery has recently drawn attention as a power source of a small portable electronic device. It uses an organic electrolyte solution and thereby has a discharge voltage twice as high as a contemporary battery using an alkali aqueous solution, and accordingly has a higher energy density.
For a positive active material of a rechargeable lithium battery, lithium-transition element composite oxides capable of intercalating lithium such as LiCoO2, LiMn2O4, LiNiO2, LiNi1−xCoxO2 (0<x<1), LiMnO2, and so on have been investigated. For a negative active material of a rechargeable lithium battery, various carbonaceous materials, such as artificial and natural graphite, and hard carbon, have been used, which may all intercalate and deintercalate lithium ions.
Positive and negative electrodes of a rechargeable lithium battery may be unstable depending on a charge state at temperature of 25° C. or more, and may thereby induce decomposition of an electrolyte salt, an organic solvent, and positive and negative active materials. This decomposition causes serious deterioration of battery stability and safety.
In order to solve these problems, an electrolyte including 0.001 to 0.1 mol/L of an organic compound having at least two cyano groups has been suggested. However, sufficient stability and safety is not realized.
High-capacity batteries are required to meet the demand of customers, while high-level stability and safety are also required. It is, however, difficult to satisfy both requirements.